ENGLISH: ILLINOIS TREES: THEIR INSECT ENEMIES 29 



The insect passes the winter as a yellow, partly grown scale 

 beneath the shell. Development is completed in early spring, and, 

 after mating, the female lays a few eggs a day. Egg laying and 

 hatching extend over a period of 6 weeks or more. Some of the 

 first-brood crawlers settle on the leaves of the elm, where de- 

 velopment is completed ; the second brood crawlers migrate back 

 to the limbs or branches for the winter. 



Control Measure 5 (end of circular). 



Elm Leaf Aphid, Myzocallis ulmifolii (Monell), fig. 22. — 

 For the most part, this aphid is a nuisance pest because of the 

 honeydew that drips on sidewalks and automobiles from the elm 

 leaves on which the aphid feeds. Following repeated foliar appli- 

 cations of DDT to elm trees, infestations of this aphid increase, 

 the secretion of honeydew increases, and some damage to in- 

 fested trees undoubtedly results. Except for sooty mold that 

 grows in the honeydew, there is no visible evidence of damage. 



Both winged and wingless forms of the yellowish-green 

 aphid, as well as white molt skins, are usually present on the 

 under sides of elm leaves. Unlike many species of aphids, the elm 

 leaf aphid does not migrate to another host. 



Control Measure 3 (end of circular). 



Woolly Elm Aphid, Eriosoma americanum (Riley). — Curled 

 elm leaves are signs of an infestation on the under sides of the 

 leaves by the white, woolly, restless aphids of this species. In- 

 festations are localized rather than general. This species over- 

 winters in the egg stage. Eggs laid on bark hatch about the 

 time elm leaves unfold; upon hatching, the aphids crawl to the 

 leaves and begin to suck juices from the tissues. In June, the 

 winged form migrates to shadbush, where it gives birth to a 

 wingless form which, in time, produces another winged form 

 that migrates back to elm to lay the overwintering eggs. 



Control Measure 3 (end of circular). 



Elm Cockscomb Gall Aphid, Colopha ulniicola (Fitch), fig. 

 23. — On an elm leaf, a conspicuous, unsightly growth resembling 

 a cock's comb is a sign of this aphid. Production of each gall is 

 stimulated by a wingless female aphid to provide a home for her 

 family. 



Control. Galls produced by aphids of this species do little 

 damage. No control measure is recommended. 



Elm Borer, Saperda tridentata Oliv., fig. 24. — Escaping sap 

 and small masses of wet, brown f rass on the trunks and limbs of 



